This invention relates to a liquid treatment system capable of removing particulate from a liquid mixture or to provide a concentrated volume of particulate using the dissolved gas flotation principle.
In engineering liquid treatment problems, many situations are encountered where the liquids are significant in volume and/or contain high amounts of particulates. Such particulates are insoluble solids, whether organic and/or inorganic, or insoluble organic liquids. Due to the high volume and nature of the particulates, on many occasions the liquids are not amenable to treatment by sedimentation because of the inability either to effect adequate removal or to provide sufficient concentration.
Prior art flotation equipment has been found unsatisfactory for increasing the loading rate with flotation basins of increased size. As used herein, the term "loading rate" means the overflow rate of input flow per surface area of the flotation basin. Manufacturers of flotation equipment have had to use lower loading rates with increasing size basins in order to maintain performance. Typical loading rates for basins less than a 200 square feet area are 2.0 to 3.0 gallons per minute per square foot. Loading rates can be less than 2.0 gallons per minute per square foot for basins approaching 500 square feet in surface area and even lower for larger basins.
Through operational experience it became evident to the inventor that design flotation basins are inlet-limiting with increasing size. Conventional flotation basins are circular or rectangular in perimeter structure. In the circular units, the size of the center inlet configuration is increased for greater flow inputs. In rectangular units, an additional number of inlet configurations are utilized. However, for either structure the inlet velocity still increases appreciably. Gas bubbles previously attached to the particles then become dislodged. Non-floating particles flow with the effluent, causing reduced effluent clarity, or fall to the basin bottom from loss of buoyancy, because the rise rate has been reduced below the overflow rate. No amount of basin capacity following the inlet will cause a significant percentage of these dislodged bubbles to reattach to the particles. In this respect, inlet conditions are irreversible in the dissolved gas flotation process as opposed to the sedimentation process where added diameter or length will offset inlet turbulence.
This creating of turbulence with greater flow in larger basins can also be theoretically illustrated with the Reynolds number. The Reynolds Number is a dimensionless term used in hydraulics to indicate turbulent flow. For liquid flow in conduits, the Reynolds number where turbulence begins is between 2000 to 4000. Reynolds Number for a flotation basin sized for 100 gpm input at a typical loading rate of 2.5 gpm/ft.sup.2 (seven ft. diameter) with a conventional center fed inlet would be on the order of 1600. This is considered non-turbulent and is satisfactory. However, a conventional flotation basin sized for 1,000 gpm at the same loading rate (approximately 22 ft. in diameter) would have an inlet Reynolds Number on the order of 10,000 or well into turbulent range. A conventional rectangular unit (typically 10 ft. wide by 40 ft. long) with multiple inlets would have inlet Reynolds Number on order of 6,000 or also well into turbulent range. A flotation unit of the same size and for the same 1,000 gpm input, but made in accordance with the principles of my invention, however, would have an inlet Reynolds Number on the order of 1,500 which is still non-turbulent range and satisfactory.
It is an object of this invention to provide a dissolved gas flotation system capable of handling increased loading rates with increasing size flotation basins.
Another object of this invention is to enhance performance and increase efficiency of a dissolved gas flotation system.
A further object of this invention is to reduce the heat velocity of a flotation basin and to decrease the discharge velocity of the inlet relative to the entrance velocity of the inlet.
It is also an object of this invention to obtain a minimum inlet velocity into a flotation basin.
Another object of this invention is to reduce the amount of bubbles too large to attach to particulates, to reduce the amount of large bubbles that would cause turbulence upon entering the flotation basin, and to reduce the amount of large bubbles that would disrupt other bubble-attached particulates in the flotation basin.
A further object of this invention is to increase the average rise rate of the particulate-carrying bubbles and to optimize the separation force of the particulate-carrying bubbles. As used herein, the term "separation force" is defined as the ratio of particulate rise rate to flow velocity.
A further object of this invention is to minimize the expansion and growth of gas bubbles so that gas bubbles that are attached to particulates do not become dislodged.
It is another object of this invention to expand the size of small bubbles, which are less buoyant than large bubbles and have only limited ability for attaching to particulates, to an efficient productive size capable of attaching to particulates before being discharged into the flotation basin.
Another object of this invention is to decrease the center well structure size in conventional circular basins, thereby increasing the capacity available for floatable separation and accumulation.
Another object of this invention is to improve effluent clarity and increase the amount of concentrated floatables.
It is also an object of this invention to circumfuse the inlet flow uniformly about the periphery of the flotation basin.
Another object of this invention is to direct the discharge flow from the periphery of the flotation basin obliquely toward the center surface.
This and other objects will become apparent from the following description and appended claims.